Composition of matter patents relating to polycarbonate and poly(ethylene terephthalate) alloys include U.S. Pat. No. 3,218,372. The alloys described in this patent contain 5 to 95 wt % polycarbonate blended with 95 to 5 wt % poly(ethylene terephthalate). Other patents pertaining to polycarbonate and poly(ethylene terephthalate) alloys include U.S. Pat. No. 4,123,473, U.S. Pat. No. 4,175,147, U.S. Pat. No. 4,230,656 and U.S. Pat. No. 4,788,251. However, none of these disclose an extrusion blow molded container produced from a high molecular weight poly(ethylene terephthalate) having a weight average molecular weight of between about 75,000 and about 85,000 blended with about 4 to about 40 wt % recycled scrap poly(ethylene terephthalate) having a weight-average molecular weight of between about 40,000 and about 55,000 and about 1.0 wt % to about 10.0 wt % polycarbonate or a polycarbonate/poly(ethylene terephthalate) concentrate as a melt strength enhancer.
Recent development work has shown that high molecular weight (weight average molecular weight of about 75,000 to about 85,000) poly(ethylene terephthalate) modified with small amounts of 1,4 cyclohexanedimethanol has sufficient melt strength for extrusion blow molding on conventional extrusion blow molding machines into containers in sizes up to about 2 liters. It would be helpful for extrusion blow mold operators to be able to use up to about 25 wt % recycled PET such as scrap from PET bottles (weight average molecular weight between about 40,000 and about 55,000), combined with neat PET when producing these containers. However, when 25 wt % to 50 wt % recycled material is combined with neat PET during the extrusion blow molding process, the melt strength is reduced significantly which makes it very difficult to hang (extrude vertically) parisons for producing containers.
It has been discovered that the melt strength of high molecular weight poly(ethylene terephthalate) containing about 25 wt % to about 50 wt % recycled scrap PET can be increased by adding a small amount of a neat polycarbonate or a mixture of about 75 to about 90 wt % polycarbonate with about 25 to about 10 wt % PET or poly(ethylene-co-3,5-1,4-cyclohexylenedimethylene terephthalate) alloy. This discovery will allow extrusion blow molders of the high molecular weight poly(ethylene terephthalate) to produce containers containing recycled PET scrap material that, otherwise, could not be done satisfactorily due to a significant decrease in melt strength when the lower molecular weight recycled material is added back to the process.
Normally, it is impossible to extrusion blow mold a large container from PET having a molecular weight in the range of 40,000 to 55,000 because of insufficient melt strength. However, if the PET is blended with a higher molecular weight neat PET and a polycarbonate in accordance with this invention, the material has sufficient melt strength to hang a parison for the extrusion blow molding process. Due to environmental concerns and public pressure, those who use containers produced from the extrusion blow moldable high molecular weight poly(ethylene terephthalate) would like to be able to use recycled poly(ethylene terephthalate) bottle scrap normally from bottles. However, when the lower molecular weight bottle scrap is combined with the higher molecular weight poly(ethylene terephthalate), the melt strength of the higher molecular weight poly(ethylene terephthalate) is reduced significantly which makes it difficult to extrusion blow mold a good quality container. Adding a small amount of neat polycarbonate or a polycarbonate/poly(ethylene terephthalate) alloy increases the melt strength of the high molecular weight poly(ethylene terephthalate)/lower molecular weight recycled PET to a level equal to or greater than that of the neat high molecular weight poly(ethylene terephthalate) which results in sufficient melt strength to produce good quality containers.